package behavioral.visitor;

/**
 * 访问者模式
 * 稳定的数据结构和易变的操作耦合问题。
 */
interface ComputerPart {
    public void accept(ComputerPartVisitor computerPartVisitor);
}

class Keyboard  implements ComputerPart {

    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        computerPartVisitor.visit(this);
    }
}


class Monitor  implements ComputerPart {

    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        computerPartVisitor.visit(this);
    }
}


class Mouse  implements ComputerPart {

    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        computerPartVisitor.visit(this);
    }
}


class Computer implements ComputerPart {

    ComputerPart[] parts;

    public Computer(){
        parts = new ComputerPart[] {new Mouse(), new Keyboard(), new Monitor()};
    }


    @Override
    public void accept(ComputerPartVisitor computerPartVisitor) {
        for (int i = 0; i < parts.length; i++) {
            parts[i].accept(computerPartVisitor);
        }
        computerPartVisitor.visit(this);
    }
}

interface ComputerPartVisitor {
    public void visit(Computer computer);
    public void visit(Mouse mouse);
    public void visit(Keyboard keyboard);
    public void visit(Monitor monitor);
}

class ComputerPartDisplayVisitor implements ComputerPartVisitor {

    @Override
    public void visit(Computer computer) {
        System.out.println("Displaying Computer.");
    }

    @Override
    public void visit(Mouse mouse) {
        System.out.println("Displaying Mouse.");
    }

    @Override
    public void visit(Keyboard keyboard) {
        System.out.println("Displaying Keyboard.");
    }

    @Override
    public void visit(Monitor monitor) {
        System.out.println("Displaying Monitor.");
    }
}


class VisitorPatternDemo {
    public static void main(String[] args) {

        ComputerPart computer = new Computer();
        computer.accept(new ComputerPartDisplayVisitor());
    }
}